The present invention relates to electrophotographic continuous form printers, and more specifically to an apparatus and control system for maintaining a constant paper tension between two paper feeding elements of a printer.
Conventionally, continuous form printers using an electrophotographic printing device feed the continuous form sheet by means of a tractor. It is desirable to maintain a constant level of paper tension between the tractor and a set of fixing rollers which fix a toner image, in order to keep the paper smooth and ensure a stable fixing operation.
However, the fixing rollers are subject to wear and slippage, and may undergo variations in diameter due to heat expansion. Furthermore, different thicknesses of paper may be used in the printer. From each of these factors, the feeding speed or tension level may undergo variation. Direct feedback control of the speed of the paper or the speed of the driving rollers or tractor may not control the tension level of the paper satisfactorily, and is unresponsive to wear, slippage, roller diameter changes, or paper thickness changes.
For these reasons, there exists a need for an electrophotographic continuous form printer that is able to satisfactorily control a level of paper tension leading into a set of fixing rollers.